Help Needed For Transaction Support In SQL Server 2005

Hi,

I have 2 stored procedure 1st insert the data in parent tables and return the Id. and second insert child table data using that parent table id as paramenter. I have foreign key relationship between these two tables also.

my data layer methods somewhat looks like

public void Save(order value)
{
using (TransactionScope transactionScope = new TransactionScope(TransactionScopeOption.Required))
         {
              int orderId =  SaveOrderMaster(value);
            value.OrderId = orderid;
              int childId = SaveOrderDetails(value);
             //complete the transaction
              transactionScope.Complete();
        }
}


here
 1. SaveOrderMaster() calls an stored procedure InserOrderData which insert a new record in order table and return the orderId  which is identity column in Order table.

2. SaveOrderDetails() call another sotored procedure which insert order details in to table "orderdetail" using the foreign key "orderid".

My Problem:
Some time the above method works correctly but when i call it repeatledly (in a loop) with data,  some time it gives me foreign key error which state that orderid is not existsin table Order. This will happen only randomly. I am not able to figureout the reason. does some one face the same problem. if yes, what could be the reason and/or solution.